Preliminary search for a νirus in Dacus oleae Gmel. populations in Northern Greece

Στην περίοδο από Ιούλιο έως Δεκέμβριο 1984 συλλέχΟησαν 4.5 g ακμαίων, 8.5 g υγιών προνυμφών και 0.45 g νεκρών προνυμφών του εντόμου Dacus oleae Gmel. από περιοχές της Βόρειας Ελλάδας, που χαρακτηρίζονταν από Βαριά προσβολή των ελαιοδένδρων από δάκο, στα οποία δεν εφαρμόστηκε χημική καταπολέμηση. Τα δείγματα εξετάσθηκαν για εγκλεισμένους και μη εγκλεισμένους ιούς με τη χρησιμοποίηση φυγοκεντρήσεων, οπτικού και ηλεκτρονικού μικροσκοπίου, ανάλυσης νουκλεϊ νικών οξέων KUI πειράματα μολυσματικότητας. Στα δείγματα των νεκρών προνυμφών, και σε αντίθεση με εκείνα των υγιών προνυμφών και των ακμαίων, εντοπίσθηκαν και απομονώθηκαν ιόμορφα σωμάτια. Τα σωμάτια αυτά είχαν διάμετρο περίπου 35 nm και μερικά ήταν άδεια, όπως φάνηκε από τη διείσδυση της χρωστικής κατά την αρνητική χρώση. Δεν κατέστη δυνατός ο παραπέρα χαρακτηρισμός των «ιοσωματίων» για το λόγο έλλειψης αρκετής ποσότητας δείγματος, ενώ προσπάθειες πολλαπλασιασμούτους σε προνύμφες του λεπιδόπτερου Galleria mellonella και σε καλλιέργειες κυττάρων Drosophila melanogastcr αποδείχθησαν ανεπιτυχείς. Αν και τα μικρά ιόμορφα σωμάτια ήταν το μοναδικό πιθανό παθογόνο αίτιο που αναγνωρίστηκε στις νεκρές προνύμφες, φαίνεται κάπως απίθανο να αποτελούν και το μοναδικό αίτιο του θανάτου για το λόγο του σχετικά μικρού αριθμού τους. Πάντως αν καταστεί δυνατό να πολλαπλασιασθούν οι «ιοί» αυτοί σε εκτροφές του δάκου της ελιάς ή σε καλλιέργειες κυττάρων ιστών του ίδιου εντόμου, ίσως να αποτελέσουν στο μέλλον ένα βιολογικό μέσο καταπολέμησης του.A large number of larvae of Dacus oleae were collected from infested olives in Northern Greece, and a small proportion of these were found to be dead. Adult flies were caught in McPhail traps at the same locations. The larvae and adults were fractionated by a series of steps designed to identify occluded and nonoccluded viruses. Virus-like particles were identified in small amounts only in the dead larvae

The Stromlo Missing Satellites Survey

The Stromlo Missing Satellites (SMS) program is a critical endeavor to investigate whether cold dark matter cosmology is flawed in its ability to describe the matter distribution on galaxy scales or proves itself once again as a powerful theory to make observational predictions. The project will deliver unprecedented results on Milky Way satellite numbers, their distribution and physical properties. It is the deepest, most extended survey for optically elusive dwarf satellite galaxies to date, covering the entire 20,000 sq deg of the Southern hemisphere. 150TB of CCD images will be analysed in six photometric bands, 0.5-1.0 mag fainter than SDSS produced by the ANU SkyMapper telescope over the next five years. (For more details see: http://msowww.anu.edu.au/~jerjen/SMS_Survey.html)Comment: 4 pages, 1 figure, in "Galaxies in the Local Volume" (Sydney, 8-13 July 2007), eds B. Koribalski and H. Jerjen, Springer Astrophysics and Space Science Proceedings, p. 18

Do the Unidentified EGRET Sources Trace Annihilating Dark Matter in the Local Group?

In a cold dark matter (CDM) framework of structure formation, the dark matter haloes around galaxies assemble through successive mergers with smaller haloes. This merging process is not completely efficient, and hundreds of surviving halo cores, or {\it subhaloes}, are expected to remain in orbit within the halo of a galaxy like the Milky Way. While the dozen visible satellites of the Milky Way may trace some of these subhaloes, the majority are currently undetected. A large number of high-velocity clouds (HVCs) of neutral hydrogen {\it are} observed around the Milky Way, and it is plausible that some of the HVCs may trace subhaloes undetected in the optical. Confirming the existence of concentrations of dark matter associated with even a few of the HVCs would represent a dramatic step forward in our attempts to understand the nature of dark matter. Supersymmetric (SUSY) extensions of the Standard Model of particle physics currently suggest neutralinos as a natural well-motivated candidate for the non-baryonic dark matter of the universe. If this is indeed the case, then it may be possible to detect dark matter indirectly as it annihilates into neutrinos, photons or positrons. In particular, the centres of subhaloes might show up as point sources in gamma-ray observations. In this work we consider the possibility that some of the unidentified EGRET $\gamma$-ray sources trace annihilating neutralino dark matter in the dark substructure of the Local Group. We compare the observed positions and fluxes of both the unidentified EGRET sources and the HVCs with the positions and fluxes predicted by a model of halo substructure, to determine to what extent any of these three populations could be associated.Comment: 12 Pages, 4 figures, to appear in a special issue of ApSS. Presented at "The Multiwavelength Approach to Unidentified Gamma-Ray Sources" (Hong Kong, June 1 - 4, 2004; Conference organizers: K.S. Cheng and G.E. Romero

Mirror Matter as Self Interacting Dark Matter

It has been argued that the observed core density profile of galaxies is inconsistent with having a dark matter particle that is collisionless and alternative dark matter candidates which are self interacting may explain observations better. One new class of self interacting dark matter that has been proposed in the context mirror universe models of particle physics is the mirror hydrogen atom whose stability is guaranteed by the conservation of mirror baryon number. We show that the effective transport cross section for mirror hydrogen atoms, has the right order of magnitude for solving the ``cuspy'' halo problem. Furthermore, the suppression of dissipation effects for mirror atoms due to higher mirror mass scale prevents the mirror halo matter from collapsing into a disk strengthening the argument for mirror matter as galactic dark matter.Comment: 6 pages; some references adde

Decaying Dark Matter can explain the electron/positron excesses

PAMELA and ATIC recently reported excesses in e+ e- cosmic rays. Since the interpretation in terms of DM annihilations was found to be not easily compatible with constraints from photon observations, we consider the DM decay hypothesis and find that it can explain the e+ e- excesses compatibly with all constraints, and can be tested by dedicated HESS observations of the Galactic Ridge. ATIC data indicate a DM mass of about 2 TeV: this mass naturally implies the observed DM abundance relative to ordinary matter if DM is a quasi-stable composite particle with a baryon-like matter asymmetry. Technicolor naturally yields these type of candidates.Comment: 20 pages, 7 figure

Dark Matter signals from Draco and Willman 1: Prospects for MAGIC II and CTA

The next generation of ground-based Imaging Air Cherenkov Telescopes (IACTs) will play an important role in indirect dark matter searches. In this article, we consider two particularly promising candidate sources for dark matter annihilation signals, the nearby dwarf galaxies Draco and Willman 1, and study the prospects of detecting such a signal for the soon-operating MAGIC II telescope system as well as for the planned installation of CTA, taking special care of describing the experimental features that affect the detectional prospects. For the first time in such a study, we fully take into account the effect of internal bremsstrahlung, which has recently been shown to considerably enhance, in some cases, the gamma-ray flux at the high energies where Atmospheric Cherenkov Telescopes operate, thus leading to significantly harder annihilation spectra than traditionally considered. While the detection of the spectral features introduced by internal bremsstrahlung would constitute a smoking gun signature for dark matter annihilation, we find that for most models the overall flux still remains at a level that will be challenging to detect unless one adopts rather (though by no means overly) optimistic astrophysical assumptions about the distribution of dark matter in the dwarfs.Comment: 10 pages, 4 figures, minor changes, matches the published version (JCAP

Quantum radiation pressure on a moving mirror at finite temperature

We compute the radiation pressure force on a moving mirror, in the nonrelativistic approximation, assuming the field to be at temperature $T.$ At high temperature, the force has a dissipative component proportional to the mirror velocity, which results from Doppler shift of the reflected thermal photons. In the case of a scalar field, the force has also a dispersive component associated to a mass correction. In the electromagnetic case, the separate contributions to the mass correction from the two polarizations cancel. We also derive explicit results in the low temperature regime, and present numerical results for the general case. As an application, we compute the dissipation and decoherence rates for a mirror in a harmonic potential well.Comment: Figure 3 replaced, changes mainly in Sections IV and V, new appendix introduced. To appear in Physical Review

Towards a synthetic tutor assistant: The EASEL project and its architecture

Robots are gradually but steadily being introduced in our daily lives. A paramount application is that of education, where robots can assume the role of a tutor, a peer or simply a tool to help learners in a specific knowledge domain. Such endeavor posits specific challenges: affective social behavior, proper modelling of the learner’s progress, discrimination of the learner’s utterances, expressions and mental states, which, in turn, require an integrated architecture combining perception, cognition and action. In this paper we present an attempt to improve the current state of robots in the educational domain by introducing the EASEL EU project. Specifically, we introduce the EASEL’s unified robot architecture, an innovative Synthetic Tutor Assistant (STA) whose goal is to interactively guide learners in a science-based learning paradigm, allowing us to achieve such rich multimodal interactions